HSPA5 and Familial prostate cancer: Considering polycationic polyarginine CPPs also enable stable and reversible ionic interactions with gene (e.g., siRNA) therapeutics, the GRP78‐targeting polyarginine peptide (W1‐R9) may also be applicable to siRNA delivery and silencing activity in the GRP78‐overexpressing DU145 prostate cancer cells (Figure 1).